The present invention relates to a contour decoding apparatus for decoding contour information encoded by a chain code.
A great amount of research and development is directed to digital video and audio service. Particularly, a bidirectional multimedia service using a communication channel is under active development. A digital video service via a bandwidth-limited communication channel requires a high compression rate. It is difficult to obtain such a high compression rate using a block-based motion compensation and transformation coding method such as existing MPEG (Motion Pictures Experts Group)-1 and MPEG-2. Since the encoding method in the existing MPEG-1 and MPEG-2 is based on a block structure of images, it is not easy to perform a flexible and independent encoding of each object or region according to a required compression rate. Thus, it is necessary to divide a given image into objects which can each be independently processed. An independent encoding of each region or object, called "object-based encoding", requires a description of the object shape. The shape information is transmitted to a decoder as contour information.
A chain coding method is known as a general lossless contour information encoding method. The chain coding method represents the contour using eight direction vectors as shown in FIG. 1A. First, the chain coding method selects a location of a starting contour pixel from which to start scanning the contour. Contour pixels are pixels constituting the contour. A chain-coding example is shown in FIG. 1B. Horizontal and vertical coordinate values of the start pixel are transmitted for the start pixel which starts a chain coding. Since the coordinate values of the start pixel occupy a relatively high ratio of transmission amount in case of a medium requiring a low transmission rate, an additional compression is required. Thus, the horizontal and vertical coordinate values of the start pixel are variable-length-coded and transmitted, or any one of the horizontal and vertical coordinate values of the start pixel is independently variable-length-coded and a difference value between the other coordinate value and the independently variable-length-coded coordinate value is variable-length-coded and transmitted.
Therefore, it is important to have an efficient decoding apparatus to decode the compressed starting location and chain codes.